Aging is associated with increased risk for heart disease, diabetes and physical disability. In women, the incidence of these age-related conditions increases dramatically after menopause. This has led to the hypothesis that ovarian hormone deficiency contributes to these adverse health outcomes. However, the effect of ovarian hormone deficiency, per se, on risk factors for disease and disability has not been clearly defined. Thus, the primary goal of the proposed studies is to characterize the effect of ovarian hormone deficiency on glucose, insulin, fat and protein metabolism. Our overall hypothesis is that ovarian hormone deficiency alters substrate turnover and utilization in a manner that increases the risk for developing chronic disease and disability. Specifically, alterations in glucose, insulin and fat metabolism increase the risk for developing heart disease and diabetes and changes in protein metabolism reduce lean tissue mass which, in turn, promotes disability. To address our hypothesis, we will measure substrate metabolism using stable isotope tracer methodology in healthy, premenopausal women before and after pharmacological ovarian suppression. Women will be randomized to receive the gonadotropin-releasing hormone agonist leuprolide acetate or placebo. Measurements of substrate metabolism will be performed during both the follicular and luteal phases of the menstrual cycle prior to treatment and 2 months after the initiation of treatment. This experimental paradigm will enable us to investigate the effect of ovarian hormone deficiency, per se, on substrate metabolism without the confounding factors present in prior cross-sectional, longitudinal and hormone replacement studies. This application consists of 3 separate experiments that will employ this model of ovarian suppression. Experiment I will investigate the effect of ovarian hormone deficiency on the glucose and insulin response to hyperglycemia. Experiment 2 will examine the role of ovarian hormone deficiency in the regulation of whole-body lipolysis under postabsorptive and epinephrine-stimulated conditions. Experiment 3 will examine the effect of ovarian hormone deficiency on whole-body protein metabolism under postabsorptive and simulated-postprandial conditions. Our findings will have direct relevance to understanding the fundamental role of ovarian hormone deficiency in the physiologic and metabolic changes that occur with menopause.